Performance of the WRB 2 cannot be considered in isolation from the cladding system with which it is used, nor can the cladding system be considered in isolation from the nature of the whole wall assembly. Yet, to discuss performance of WRB in the system we need first to be able to characterise the material alone. In this paper, therefore, we take a step back and introduce the material classification and performance characterization in respect to the field performance of the WRB products. The prime function of a WRB is to shed water that may penetrate the cladding. A secondary function includes the reduction of airflow through walls, while allowing the water vapour to escape from the inside of the wall. One could therefore think that the test methods used for determination of critical material properties such as air, vapour, and liquid permeability coefficients for these materials are not questioned. Yet, this is not the case. This paper, second in the series, reviews the results of hygric tests conducted on various fresh and weathered WRB products. At this stage, the work did not aim at evaluating performance of the WRB products under various climatic conditions, but rather at examination of utility of new evaluation methodology that is proposed here. This evaluation methodology is for generating information on the basis of which such judgments might be made in the future. Weather resistive barriers, alternatively called water resistive barriers (WRB) perform many different functions in a building envelope. Typically, the WRB serves as a second line of defense in water penetration control. In this chapter, the authors take a step back and introduce the material classification and performance characterization in respect to the field performance of the WRB products. They review the results of hygric tests conducted on various fresh and weathered WRB products. A classification of the WRB products in accordance with the following five classes: Type C Asphalt-impregnated cellulose fiber based WRB, Type P Polymeric fibrous WRB, Type PP Perforated polymeric film, Type LA Liquid-applied WRB, Type MF Micro-porous film WRB. Typically, the liquid applied WRB are used either in plant- or in the field manufactured wood-based, composite sheathing. Two types of penetrations were tested: nails used to fasten a metal reinforcement to the substrate and staples used to fasten the WRB to the OSB or plywood substrate.